The present invention relates stringing cable through conduits, more particularly, the present invention relates to a cable feeding sheave assembly for installing cable within conduits.
Conduit sheaves are devices used to install cable within underground conduits, such as those accessed within manholes and commercial buildings. Conduit sheaves are sized to fit within the conduit. Commercially available conduit sheaves use aluminum sheave wheels. These aluminum wheels tend to wear out quickly and damage the conductor cable being installed.
A significant problem with conduit sheaves is that they do not provide a mechanism for securing the device within the conduit. While cable is being installed, tension holds the conduit sheave in place. However, when the cable becomes slack during installation, the conduit sheave can shift within the conduit or fall out of the conduit (particularly with an overhead conduit), causing potential damage to the cable, human injury, and delay in the installation process.
It would be a significant advancement in the art to provide a conduit sheave having a wheel which overcomes the problems with aluminum wheels described above. It would also be an advancement in the art to provide a conduit sheave which can be quickly, temporarily secured within the conduit.
The present invention is directed to a conduit cable feeding sheave assembly. The cable feeding sheave has a frame structure, an axle assembly disposed within the frame structure, and a sheave wheel disposed about the axle assembly. A slotted, tubular arm affixed to the frame extends along a line substantially tangential to the wheel. The arm has an exterior diameter sized to fit within a conventional conduit pipe. The typical conduit size ranges from about 2 to 10 inches, and more preferably between about 3 and 6 inches. The slotted, tubular arm facilitates loading and unloading the cable within the cable feeding sheave assembly.
In a presently preferred embodiment, the tubular arm has at least one locking mechanism for temporarily securing the conduit sheave assembly within the conduit pipe. One preferred locking mechanism is a threaded screw that extends through the interior of the tubular arm to engage the inside surface of the conduit. One or more screws can be used for this purpose. Examples of some possible alternative locking mechanisms that can be used include a lever actuated cam, a sliding wedge assembly, and a friction collar.
In a presently preferred embodiment, the sheave wheel is fabricated of a non-conducting, self-lubricating, durable polymeric material. In a preferred embodiment the polymeric material has a coefficient of friction less than 0.5. A variety of engineering plastics can be used, particularly those containing nylon. One currently preferred polymeric material is PA6-G-type nylon.
In a preferred embodiment, one or more handles are affixed to the frame structure to facilitate transport and positioning of the block assembly.